Heating, ventilating, and air conditioning (HVAC) systems commonly employ units such as condensers and compressors for performing applications such as cooling and heating air. Compressors are typically driven by induction motors that operate using power supplied from an electrical grid via power lines. During peak periods in which the overall demand for power is relatively high, the electrical grid voltage may be reduced. In brownout situations, for example, the supply of voltage across power lines may be significantly reduced as an attempt to prevent blackouts. If a compressor is forced to operate at reduced voltage levels for a prolonged duration, the compressor may eventually stall. In this case, the compressor draws higher current, thereby increasing the operating temperature while reducing the line voltage (e.g., from about 240 volts to about 170 volts).
To protect the compressor from damage due to thermal overload conditions, a protection device may be configured to deactivate the compressor. However, the time necessary to trigger such protection devices may be multiplied when compressors stall at reduced line voltages such as 170 volts or less. For instance, it may take a protection device about three to five times longer to trip the compressor in these situations, and therefore, the protection device may be unable to prevent thermal damage to the compressor.
Furthermore, when multiple compressors go offline due to situations such as brownouts, many of the compressors may return online at similar times. In such situations, the compressors may draw substantial quantities of current, thereby reducing the line voltage as described above. As a result, widespread power outages may occur if the electrical grid cannot satisfy the overall demand. Similarly, when compressors attempt to simultaneously return online once power is restored following a blackout, a subsequent blackout may occur due to the excessive power demanded to restart the compressors.